Powderless etching bath compositions

ABSTRACT

IMPROVED POWDERLESS ETCHING BATH ADDITIVES COMPOSITTIONS, ESPECIALLY FOR ETCHING MAGNESIUM PHOTOENGRAVING PLATES, COMPRISING: (A) AT LEAST ONE WATER-SOLUBLE OR WATER-DISPERSIBLE SULFORNATED FATTY ACID OF FROM 8 TO 24 CARBON ATOMS, WHEREIN THE SULFUR ATOM IN THE SULFONATE GROUP IS DIRECTLY BONDED TO A CARBON ATOM, AND (B) AT LEAST ONE SATURATED OR OLEFINICALLY UNSATURATED MONOCARBOXYLIC ACID OF FROM 8 TO 24 CARBON ATOMS, AND (C) AT LEAST ONE LOWER MONOCARBOXYLIC ACID OF FROM 2 TO 6 CARBON ATOMS AND FOR POLYCARBOXYLIC ACID OF FROM 2 TO 10 CARBON ATOMS, AND ETCHING BATHS CONTAINING SUCH COMPOSITIONS AND NITRIC ACID AND WATER, GIVE GOOD ETCHING PERFORMANCE, PARTICULARLY IMPROVED DEFINITION OF THE PRINTABLE AREA OF THE PLATE, DEPTH OF HALF-TONES, AND SIDEWALL SMOOTHNESS.

United States Patent 3,725,159 POWDERLESS ETCHING BATH COMPOSITIONS Harold J. Messerschmidt, Stockholm, Karl Heyman, Moutclair, and Bernadou W. Johnsen H, Paterson, NJ., assignors t0 Mona Industries, Inc., Paterson, NJ. N0 Drawing. Filed Mar. 29, 1972, Ser. No. 239,385 Int. Cl. B44n 3/02; C23g 1/26 US. Cl. 156-14 21 Claims ABSTRACT OF THE DISCLOSURE Improved powderless etching bath additive compositions, especially for etching magnesium photoengraving plates, comprising:

(a) at least one water-soluble or water-dispersible sulfonated fatty acid of from 8 to 24 carbon atoms, wherein the sulfur atom in the sulfonate group is directly bonded to a carbon atom, and

(b) at least one saturated or olefinically unsaturated monocarboxylic acid of from 8 to 24 carbon atoms, and

(c) at least one lower monocarboxylic acid of from 2 to '6 carbon atoms and for polycarboxylic acid of from 2 to 10 carbon atoms;

and etching baths containing such compositions and nitric acid and water, give good etching performance, particularly improved definition of the printable area of the plate, depth of half-tones, and side wall smoothness.

This invention relates to powderless etching and is more specifically concerned with improved additive compositions, both anhydrous and water based, for use in powderless etching baths. In further aspect, the invention relates to etching baths as such, particularly for chemically dimensioning photoengraving plates, and with a method of etching such plates, especially magnesium-based plates.

To make photoengraving plates a flat or cylindrical plate of an acid-soluble metal such as magnesium, zinc or one of their alloys, is coated with a light sensitive coating or enamel. This coated surface is exposed to light through a negative having an image thereon so as to produce an image on the coating. The exposed coated surface is then developed to form an acid-resistant coating corresponding to the image produced by exposure. This coating may be further hardened by heating and the final acid-resistant image is called the resist. Subsequently, the image bearing surface of the plate is subjected to etching by an acid to remove the metal which is not under the resist and thus to produce the image in relief.

In carrying out this etching process, techniques are employed to reduce lateral etching which undercuts the resist and/or the relief side walls, which undercutting may cause a weakening, distortion or complete loss of image.

A common method which the art formerly used for minimizing lateral etching consisted of powdering the sides of the relief with an acid-resistant powder, but this was a difiicult and time-consuming operation which had to be repeated a number of times during the etching of each plate.

In recent years so-call-ed powderless etching has been introduced and explained. In this technique the etching bath is so formulated that the non-resist portion of the I plate can be removed without the need for powdering the side walls.

Powderless etching is now a well-known, widely practiced technique. It is used to etch photoengraving plates and other similar shaped articles. Zinc, magnesium and a1- loys based thereon are generally used as the photoengraving plate metals.

In the growth of this art, it has been discovered that ice:

etching baths made up of aqueous solutions of nitric acid and one or more surfactants are quite suitable for powderless etching or zinc and/or magnesium. Many technological contributions have been made to this art, such as for example in US. Pats. 2,640,673; 2,640,764 and 2,640,766, according to which the aqueous nitric acid etching baths are modified by the incorporation therein of aliphatic acids, or esters of aliphatic acids with polyhydric aliphatic alcohols, 01' sulfonates of succinic acid diesters.

One characteristic of these etching baths is their tendency to permit localized defilming on relief side walls. This results in a chipped surface which, in aggravated situations, causes poor printing plates. Another problem stems from the inability of these same baths to quickly form a protective film in the initial stage of etching that will protect the resist from lateral etching beneath it. Further, as the etching action of the acid penetrates to greater depths, there is a problem of preventing lateral etching of relief side walls. Another problem of great importance is the capacity of the etching bath to produce proper depths of etch in all areas of a combination plate, i.e., a plate having both line and half tone image areas. This latter problem, for example, is not vexing because the use of filming additives which may be expected to increase or stabilize the filming tendency of the etching bath usually also results in the production of lesser depths of etch in half tone areas of combination plates. On the other hand, while the use of smaller amounts of the filming additives might be expected to provide deeper etching in half tone areas, such modifications also tend to cause excessive etching and undercutting in open line areas of the same plate. These problems are often sufficiently serious to make the poor products which result therefrom readily apparent to even the casual observer, particularly as evidenced by a chewed appearance of the plate.

Many attempts have been made to remedy the situation and to formulate etching baths which will give acceptable etching speeds and good quality production. Thus, in more recent patents than those set forth above, newer and improved formulations have been disclosed, which employ a water-immiscible organic liquid. Thus the modern etching bath technology is generally based on aqueous nitric acid, a water-immiscible organic liquid and a surfactant. These modern etching baths have reached a high degree of commercial success and are in wide use throughout the world. Unfortunately, these modern etching baths still have a problem in that they are ecologically undesirable. The water-immiscible organic liquid, which is generally a petroleum solvent, is a serious pollutant. It is therefore desirable to eliminate this component from etching bath compositions or at least to reduce the level thereof as much as possible.

The most commonly commercially used surfactant in the powderless etching art is a material which is usually referred to in the trade as sulfonated castor oil. This is a commercially available material which is chemically mis-named. The material referred to is actually a sulfated castor-oil, mainly the sulfate ester of ricinoleic acid (that is, the hydroxyl group of ricinoleic acid is esterified with sulfuric acid to add a sulfate group thereon). Other surfactants which have been recommended in the patent literature in combination with the water-immiscible organic liquid are sulfosuccinates, petroleum :sulfonates, alkylaryl sulfonates, sulfated alcohols, sulfated fats and oils other than sulfated castor oil, phosphates, esters, polyether non-ionic surfactants, and alkylaryl ether sulfonates.

It is, therefore, an object of this invention to provide a novel etching bath for zinc or magnesium based shaped articles such as photoengraving plates.

It is another object of this invention to provide an improved etching bath having markedly improved filming capacity and giving better side wall protection and decreased lateral etching.

It is a further object of this invention toprovide a novel additive for use in aqueous nitric acid etching baths.

Other objects of this invention are to provide a novel etching bath capable of producing desired depths of etch in all kinds of image areas of combination plates, to provide an etching bath capable of forming a stable protective film to prevent or retard lateral etching and chipping of relief side walls and a smooth, uniform side wall permitting easy release from a matrix, besides having visual appeal.

A still further object of this invention is to provide an improved etching bath for producing name plates, metal patterns, templates and the like.

In accordance with this invention there is provided an additive composition comprising:

(a) from about to 90 percent by weight of at least one Water-soluble or water-dispersible anionic aliphatic sulfonated carboxylic acid containing at least one hydrophobic hydrocarbon group of from 8 to 24 carbon atoms attached to the carboxyl group and at least one sulfonate group attached to a carbon atom in said hydrophobic hydrocarbon group,

(b) from about 5 to 90 percent by weight of at least one saturated or olefinically unsaturated monocarboxylic acid of from 8 to 24 carbon atoms, and

(c) from about 5 to 90 percent by weight of at least one saturated or olefinically unsaturated (i) lower mono-carboxylic acid of from 2 to 6 carbon atoms and/ or (-ii) lower poly-carboxylic acid of from 2 to carbon atoms.

While compositions containing components (a) and (b), as identified above, show substantial improvement relative to prior etching additives and bath compositions, the addition of component (c) appears to synergistically improve the definition of the printable area of the etched plate. Use of the compositions of this invention in etching also results particularly in improving the depth of halftones and improving cleaning action, such as eliminating irregularities, e.g., bottom dirt, on the relief areas. The etch factor ratios achieved by use of component (0) are unexpectedly higher than those of compositions not containing this ingredient.

Apart from providing the additive compositions described above, the instant invention provides etching bath compositions comprising components (a), (b), and (c) and, additionally, water and a mineral acid. In such a bath, component (a) is preferably contained in an amount of from 0.5 to 10, most preferably from 2 to 6, grams per liter of final bath. Component (b) is preferably contained in an amount of from 0.5 to 10, most preferably from 2 to 8, grams per liter of final bath. Component (c) is preferably contained in an amount of from 0.5 to 100, more preferably from 1 to 60 and most preferably from 2 to 30, grams per liter of final bath.

The mineral acid of an etching bath is generally nitric acid, although mixtures of nitric acid and small quantities of sulfuric, hydrochloric or acetic acids can be beneficial. Suitable amounts of mineral acid range from about 30 to 300 grams per liter of bath with a preferred range from about 70 to 250 grams per liter of bath. The mineral acid component of the powderless etching bath of this invention is known per se.

The sulfonated carboxylic acids used as component (a) in this invention are true sulfonates as distinguished from the so called sulfonated oils like sulfonated castor oil which products are actually sulfates or esters of sulfuric acid. The true sulfonates of this invention differ from the sulfates by the fact that, in the sulfonate, sulfur is directly linked to a carbon atom rather than through an intermediary oxygen atom as in the sulfate.

Examples of fatty acids which in their sulfonated condition are useful in this invention are, for example, caprylic, capric, lauric, myristic, palmitic, stearic, isostearic, behenic, lignoceric acids, undecylenic, myristicoleic, palmitoleic, oleic, linoleic, linolenic, eleo-stearic, arachidonic acids and the like. Saturated and unsaturated fatty acids which have substituents on their hydrocarbon chains can also be sulfon-ated to add a sulfonate substituent bonded to a carbon atom thereof. Examples of such acids are ricinoleic, 9,10-dichlorostearic acids, betaphenylpropionic, IO-phenylundecanoic and 9,10-dibenzylstearic acids. In many cases the esters, amides and nitriles, chlorides and/or anhydrides of these fatty acids can be sulfonated with ease, and the sulfonation products thus produced are applicable in this invention provided there is a sulfur-carbon bond and provided they hydrolyze in an aqueous acid etching bath into the corresponding sulfonated carboxylic acids. The sulfonated acids of this invention can be based on pure fatty acids or can be mixtures of fatty acids and/or esters or other derivatives thereof such as occur naturally in vegetable, animal or marine oils, fats and waxes or in synthetic fatty acids derived from petroleum, bituminous coal and natural gas. Where mixtures of sulfonated fatty acids are to be used, sulfonation of the fatty acids can be accomplished before and after mixing.

The sulfonation of fatty carboxylic acids is a Well established procedure and can be accomplished by different means as the occasion demands. Saturated fatty acids can be sulfonated directly in the alpha-position by reaction thereof with chlor-sulfonic acid or sulfur trioxide, which may be dissolved in sulphur dioxide, dioxane or chlorinated hydrocarbons. Alpha-sulfonations can also be accomplished less directly by the Strecker reaction of an alpha-bromo fatty acid with sodium sulfite. Side chain sulfonation of phenylalkanoic acids like 4-phenylcaproic, IO-phenylundecanoic, phenylstearic and 9,10-dibenzylstearic acids can be performed with a dioxane-sulfur trioxide complex. The same method is used for the alphasulfonatio'n of hydroxystearic and 9,10-dihydroxystearic acid. Monoand polyunsaturated fatty acids having hydrocarbon chains in the range of 8 to 24 carbon atoms can be sulfonated with sulfur trioxide dissolved in sulfur dioxide to yield truly sulfonated carboxylic acids e.g., oleic acid yields predominantly 8-, 9-, 10-, or ll-sulfooleic and 9-hydroxy-l0-sulfostearic acids when reacted with a stoichiometric amount of sulfur trioxide (see US. Pat. 2,743,288 to Rueggeberg et al.). As taught in the Rueggeberg et a1. patent, the sulfo group attaching to the fatty acid, e.g., oleic acid, may attach on one or more different positions; thus, in the case of the sulfo-oleic acid produced according to Rueggeberg et al., the reactio-n product appears to be a mixture of predominantly 8-, 9-, 10-, or ll-sulfo-oleic acid (as well as some 9-hydroxy-10- sulfostearic acid). For convenience hereinafter the term ll-sulfo-oleic acid is sometimes used; in using this term we intend to refer to the mixed product obtained by following the teachings of the art. Truly sulfonated ricinoleic acid can also be obtained by sulfonation with acetyl sulfonic acid, which is itself obtained by reacting sulfur trioxide with glacial acid or acetic anhydride.

The monocarboxylic acids used as component (b) in this invention may be straight-chain, linear, or branchedchain and preferably contain from 8 to 18 carbon atoms. Preferably, said acids have melting points below 50 C. and, most preferably, they are liquids at room temperature.

Exemplary of the monocarboxylic acids which may be used are both saturated acids and unsaturated acids such as caprylic, capric, lauric, myristic, palmitic, stearic, isostearic, behenic, lignoceric acids, undecylenic, oleic, linoleic, linolenic, eleostearic, arachidonic acids and the like. Thus, it can be seen that the acids operative as component (b) are generally the same as those used, in sulfonated form, as component (a). Thus, saturated and unsaturated fatty acids which have substituents on their hydrocarbon chains can also be used. Examples of such acids are ricinoleic, 9,10-dihydroxystearic, 10-chloro-, or 9,10-dichloro'stearic acids, beta-phenylpropionic, lO-phenylundecanoic and 9,10-dibenzylstearic acids. Of the saturated acids, isostearic, caprylic and capric acids are particularly preferred, based on their melting point, ease of handling, outstanding performance in etching compositions and, of the unsaturated acids, oleic, and linoleic (one olefinic double bond) and linolen-ic (two double bonds) are preferred.

While we generally prefer to use unsubstituted acids, it will be understood by those skilled in the art that operative acids may include one or more substituents which do not essentially alter the lipophilicity of the acid molecule; thus, halogenated mono-carboxylic acids, such as bromo-, chloro-, or fluoro-substituted acids, may be employed.

It has been found useful, even preferable to use mixtures of two or more acids, e.g., the combination of caprylic and oleic acids, or of caprylic and isostearic acids as component (b) herein.

The monoor poly-carboxylic acids operative as component herein are, optionally substituted, saturated or olefinically unsaturated mono-carboxylic acids of from 2 to 6 carbon atoms or poly-, especially diand tri-, carboxylic acids of from 2 to 10 carbon atoms.

Thus, within the compass of the component (c) definition, there are simple saturated mono-carboxylic acids, preferably of from 2 to 4 carbon atoms, such as acetic and butanoic, but also hexanoic, acids, as well as unsaturated mono-carboxylic acids such as acrylic, crotonic or isocrotom'c (butenoic) acid, and saturated or unsaturated monoacids also containing a substituent, e.g., halogen, such as chloro, fiuoro, bromo, or iodo, or hydroxy or sulfo or cyano, which preferably does not substantially decrease the water-solubility of the molecule; thus, chloro-acetic is illustrative. For instance, glycolic acid, OHCH -COOH, may be employed and, interestingly, we have found that less of the hydroxy-substituted acid is needed to give the same results as the correspond ing unsubstituted acid, i.e., acetic acid, although the same final result could be achieved by use of greater amounts of the acetic acid.

Of the poly-carboxylic acids within the compass of component (c), We prefer the diand tricarboxylic materials of 2 to 10, preferably 4 to 6, carbon atoms and we prefer the triover the diacids. In addition, we prefer the triand dimaterials over the mono-carboxylic acids because of the particularly excellent results achieved by use of the poly-acids. Illustrative of the dicarboxylic acids are oxalic acid, malonic, succinic acid, glutaric acid, adipic acid, suberic acid, azaleic acid, and sebacic acid; hydroxy-malonic acid and malic acid (which are hydroxy substituted); tartaric acid (which is a di-OH acid); and maleic acid and itaconic acid (which are unsaturated diacids). Also included are, e.g., 2-hydroxy-hex-3-en-l,6- dioic acid, i.e., molecules having substitution and unsaturation. Of the tri-carboxylic acids, there may be mentioned as illustrative citric acid, and aconitic acid (which is unsaturated) and 4-hydroxy-1,2,6-hexatrioic acid. The unsaturation and substitution described above for the monoacids is thus also applicable to the diand triacids of component (0).

The acids of component (c) may, of course, be supplied in the form of salts thereof, e.g., sodium or other alkali metal salts, or ammonium or amine salts, thereof; these are then split to the free acid in the ultimate bath composition. Thus, there are contemplated as within the compass of inventive component (c) sodium succinate or ammonium itaconate, or where the acid is substituted, e.g., sodium sulfosuccinic acid and tri-sodium sulfoitaconate.

While the specific optimum amount, within the range above set forth, of component (0) in a particular use application is readily determinable by the skilled artisan, we find that, as indicated above, in the range of 0.5 to of component (e) per liter of final bath. In general, more of the monoacid is needed for the same results as of the diacid, and more of the diacid than of the triacid except when substitutions, e.g., -OH substitution, lessen the amount required, as noted above. In relation to components (a) and (b), above, few hard-and-fast generalizations may be made but we have found that, as the amount of component (a) or (b) is increased, the amount of component (c) must also be increased, assuming other factors, especially nitric acid concentration, are constant. An increased nitric acid content generally requires use of less carboxylic acid, assuming a constant concentration of components (a) and (b), for similar results.

While the precise amount of sulfonated acid (a) relative to the amount of mono-carboxylic acid (b) to be used, Within the ranges set forth above, for optimum re sults is readily determinable by the skilled artisan, it has been found that, when using the shorter alkyl chain monocarboxylic acids, less sulfonated acid (a) is required than when using the longer, e.g., 18 carbon atom and over monocarboxylic acids. Generally, however, the total amount of monocarboxylic acid (which may be a mixture of acids) will be from, e.g., 0:5 to 10 times, by weight, the amount of sulfonated acid used. This ratio, and the total amount of components (a) and (b) used in the bath, will depend also on other factors, e.g., the amount of nitric acid employed. We have found that, most preferably, from about 1 to 2 grams of sulfonated acid, and about 1 gram of mono-carboxylic acid, are employed per liter of final etching bath. The precise amount of component (0) to be used in relation to components (a) and (b) is readily determinable by the skilled artisan; we have found that when using the preferred species of components (a), (b) and (c), the Weight ratio of (c) to (a-l-b) is often preferably about 0.1 to 2, preferably, e.g. 0.5 to 2. Thus, e.g., 1 gram of citric per gram of (a) and per gram of (b) could be used; or 6 grams of citric for 2 of (a) and 1 of (b). However, this may vary greatly if other species of (a) and (b) are employed or if non-preferred amounts of (a) and (b) are used.

It will be understood by those skilled in the art that, with regard to the additive compositions which one aspect of this invention, i.e., those compositions not con taining the mineral acid and water used in the final etching bath, may desirably contain, in addition to the components (a) to (c) set forth above, a neutralizing agent such as a basic amine, e.g., diethanol amine, monoisopropanol amine and the ethylene glycol amines, for the purpose of neutralizing the acidic components included within (a) to (c) above. In further aspect of the additive compositions contemplated herein, components (a) to (c) are combined with water, and, as a neutralizing agent, appropriate amounts of an alkali metal hydroxide such as potassium hydroxide. Such additive compositions, either non-aqueous or aqueous, can be transported per se as articles of commerce and constitute an embodiment of this invention different from the ultimate etching bath compositions which also contain a mineral etching acid, e.g., nitric acid, which is a separate composition claimed herein.

It will also be understood that a number of additional ingredients may desirably be incorporated into either the additive compositions or the ultimate bath compositions envisioned herein. Thus, e.g., foam suppressants such as Triton CF 21 may desirably be added, certain mineral oils may be added as cleansing agents but care must be taken that any water immiscible organic liquid be added only in amounts of less than two grams per liter of final bath because use of greater amounts deleteriously affects etching performance when using the compositions of the instant invention. In fact, it appears that, as regards the instant invention, so-called water immiscible organic liquids are desirably only added at concentration ranges at which such liquid is in fact miscible, i.e., at very low concentrations. When used in such very small amounts it has been found that the liquid in question, e.g., white mineral oil, actually mixes with the final bath and thus can no longer be regarded as a water immiscible organic liquid.

It is truly surprising that when a typical aqueous solution of nitric acid, in a concentration which is conventionally used for zinc or magnesium plate etching, is modified by the admixture thereof with the composition comprising (a), (b) and (c) as set forth herein, the resultant etching bath is suitable for use with no waterinrmiscible organic liquid required in the composition which liquids are called for in certain prior art compositions. Although very small amounts of such liquid may be added, e.g., up to about 2 grams per liter of the final bath, use of greater amounts deleteriously affects etching performance.

In accordance with one aspect of this invention, etching baths are provided having the following composition:

Grams per liter Nitric acid (100%) 30300 Sulfonated fatty acid [Component (a)] 0.5-10 Monocarboxylic acid [Component (b)] 0.510 Carboxylic acid [Component 0.5-

Water-immiscible organic liquid 0-2.0 Water Balance 1 Citric acid, preferred 2-3 grams per liter.

In etching with the baths of the present invention it has been found to be desirable to impinge the bath against the surface to be etched, as by splashing. In theory at least, the etching bath forms a partially acid resistant film on the resist-free metal surfaces, and when the bath is impinged against the surface to be etched in a direction normal to that surface, the film is broken. On the other hand when the bath hits the side of the relief, the film is generally not broken because of insufficient striking force and etching of the sides (or under-cutting) is substantially reduced.

An etching machine of the type disclosed in US. Pat. No. 2,669,048, issued Feb. 16, 1954, and entitled iEtching Machine or the so-called bubble-etch machines as described in, e.g., U.S. Pats. Nos. 3,227,166; 3,136,323; 3,136,671 (all to C. Martz), can be used. In the machine described in, e.g., US. Pat. Nos. 3,227,166; 3,136,323; paddles dipping into the bath composition intermittently throw, by splashing, the etching bath composition in sheets upwardly against the image bearing side of the object being etched, e.g., a plate. The bubble-etch machine described in the latter group of three US. patents comprises a manifold having multiple orifices in the manifold pipes immersed in the etching bath wherein compressed air is forced through the manifold to produce bubbles which then rise upwards through the etching bath into which the plate to be etched is immersed and rotated. Other types of etching machines known to the art are also applicable.

As used in this specification, the terms etch factor ratio" (EFR) is defined as the ratio of (1) the depth of the etch adjacent to a line of resist divided by one half of the loss in width of metal immediately beneath the resist using a particular additive to (2) the depth of the etch adjacent to a line of resist divided by one half of the loss in width of metal immediately beneath the resist t/ s 2 D /W 2 EFR= Where:

D is the etch depth with additive D is the etch depth without additive W is the under cutting loss with additive W is the under cutting loss without additive The following examples are given to illustrate the present invention, but are not to be construed as limiting thereon.

EXAMPLE I An etching bath was made up consisting of 8 percent by weight of (pure) nitric acid, 0.6 percent by weight of ll-sulfo-oleic acid, 0.25 percent by weight of oleic acid and 0.40 percent by weight of oxalic acid and the balance water. This bath was used to etch magnesium printing plates having a typical, representative resist image thereon. Etching was carried out for 4 minutes at F. in a bubble-etch machine conventional in the art as described above. The quality of the etched plates was good with little lateral etching or side wall erosion being observed. The plate was open and holding well. The etch factor ratio (EFR) was about 30.

EXAMPLE II Example I was repeated but the oxalic acid was excluded, the other conditions being the same. No etch factor ratio determination was possible since the plate did not etch in its entirety.

tEXAMPLE III Example I was repeated except that the nitric acid concentration was 12 percent and, instead of the oxalic acid, 2.4 percent by weight of acetic acid was used. Results were comparable to those obtained in Example I.

EXAMPLE IV An etching bath was made up consisting of 16 percent by weight of (pure) nitric acid, 0.45 percent by weight of ll-sulfo-oleic acid, 0.35 percent by weight of caprylic acid, 1.8 percent by weight of malic acid and the balance water. This bath was used to etch magnesium printing plates having a typical representative resist image thereon. Etching was carried out for 4 minutes at 110 F. in a bubble-etch machine conventional in the art as described above. The quality of the etched plates was observed. The plate was open and holding well. The etch factor ratio (EFR) was about 30.

EXAMPLE V Example IV was repeated except that malic acid was excluded. No etch factor ratio determination was possible because the plate either did not etch or was totally blanked out under the conditions used.

EXAMPLE VI Example I was repeated but, instead of oxalic acid, 0.2 percent by weight of citric acid was used. The results were comparable to those obtained in Example I.

It is particularly noteworthy that the compositions of the instant invention, while providing outstanding etching performance, do not pose any pollution hazard, contrary to certain conventional compositions. Thus, our compositions are biodegradable as demonstrated in actual tests in which samples containing the components of this invention were tested according to standard techniques [Standard Methods for the Examination of Water and Waste Water, 13th Edition (1971), published by the American Public Health Association; tests conducted by 9 the Bridgeport Testing Laboratory, Inc.] and it was found that such compositions were 91% biodegradable after 30 days of being in the test water.

It will be understood that the specification and examples are illustrative but not limitative of the present invention and that other embodiments within the spirit and scope of the invention will suggest themselves to those skilled in the art.

What is claimed is:

1. Powderless aqueous nitric acid etching bath additive composition for etching plates of magnesium, zinc or alloys thereof; comprising:

(a) from to 90 percent by weight of a water-soluble or water-dispersible sulfonated fatty acid of from 8 to 24 carbon atoms, wherein the sulfur atom in the sulfonate group is directly bonded to a carbon atom,

(b) from 5 to '90 percent by weight of at least one saturated or olefinically unsaturated monocarboxylic acid of from -8 to 24 carbon atoms, and

(c) from 5 to 90 percent by weight of at least one saturated or olefinically unsaturated monocarboxylic acid of from 2 to 6 carbon atoms, or polycarboxylic acid of from 2 to carbon atoms,

based on the total additive composition; said composition being adapted for use at a concentration of about 1.5 to 30 gms./l. of the etching bath.

2. Powderless aqueous nitric acid etching bath additive composition for etching magnesium, zinc or alloys thereof; comprising water and, dissolved or dispersed therein, an additive comprising:

(a) from 0.5 to 90 percent by weight of a water-soluble or water-dispersible sulfonated fatty acid of from =8 to 24 carbon atoms, wherein the sulfur atom in the sulfonate group is directly bonded to a carbon atom, and

(b) from 0.5 to 90 percent by weight of at least one saturated or olefinically unsaturated mono-carboxylic acid of from 8 to 24 carbon atoms, and

(c) from 0.5 to 90 percent by weight of at least one saturated or olefinically unsaturated mono-carboxylic acid of from 2 to 6 carbon atoms, or polycarboxylic acid of from 2 to 10 carbon atoms,

based on the total additive, said composition being adapted for use at a concentration of about 1.5 to 30 grams of gheh components [(a) +(b)+(c)] per liter of the etching 3. Composition as claimed in claim 2 additionally containing a neutralizing quantity of an alkali hydroxide or an amine and wherein the composition contains at least about 50 percent by weight of water.

4. Composition as claimed in claim 1 wherein the sulfonated fatty acid component (a) is sulfo-oleic acid; the mono-carboxylic acid component (b) is caprylic, capric, lauric, myristic, palmitic, stearic, isostearic, behenic, lignoceric, undecylenic, myristoleic, palmitoleic, oleic, linoleic, linolenic, eleostearic, arachidonic, ricinoleic, 9,10 dihydroxystearic, IO-chlorostearic, 9,10-dichlorostearic, lbeta-phenylpropionic, ilO-phenylundecanoic, or 9,10-dibenzylstearic acid; and the monoor poly-carboxylic acid (0) is a mono-carboxylic acid of from 2 to 4 carbon atoms or a poly-carboxylic acid of from 4 to 6 carbon atoms; and wherein the weight ratio of component (c) to components (a+b) is from 0.121 to 2:1.

5. Composition as claimed in claim 1 wherein the carboxylic acid of component (c) is a saturated or monounsaturated mono-carboxylic acid of from 2 to 6 carbon atoms or dior tri-carboxylic acid of from 2 to 10 carbon atoms, wherein said acid may be unsubstituted or substituted with hydroxy or halogen, and wherein said acid may be supplied in the form of a salt thereof convertible to said acid in the ultimate etching bath composition.

6. Composition as claimed in claim 1 wherein the carboxylic acid of component (0) is selected from the group 10 consisting of acetic acid, lactic acid, glycolic acid, oxalic acid, malonic acid, succinic acid, malic acid, maleic acid, glutaric acid, adipic acid, sebacic acid, itaconic acid, and citric acid.

7. Composition as claimed in claim 1 wherein the carboxylic acid of component (c) is a polycarboxylic acid of from 4 to 6 carbon atoms.

'8. Composition as claimed in claim 1 wherein the carboxylic acid of component (c) is a mixture of at least two acids.

9. Composition as claimed in claim 1 wherein the carboxylic acid of component (c) is malic acid.

10. Composition as claimed in claim 1 wherein the carboxylic acid of component (c) is citric acid.

11. Powderless etching bath for etching plates of magnesium, zinc or alloys thereof comprising water and from 30 to 300 grams of nitric acid and (a) from 0.5 to 10 grams of a water-soluble or waterdispersible sulfonated fatty acid of from 8 to 24 carbon atoms, wherein the sulfur atom in the sulfonate group is directly bonded to a carbon atom, and

(b) from 0.5 to 10 grams of at least one saturated or olefinically unsaturated monocarboxylic acid of from 8 to 24 carbon atoms, and

(c) from 0.5 to grams of at least one saturated or olefinically unsaturated mono-carboxylic acid of from 2 to 6 carbon atoms or polycarboxylic acid of from 2 to 10 carbon atoms,

per liter of bath.

12. Etching bath as claimed in claim 11 wherein the sulfonated fatty acid component (a) is sulfo-oleic acid; the saturated or unsaturated mono-carboxylic acid component (b) is selected from the group consisting of caprylic, capric, launic, myristic, palmitic, stearic, isostearic, behenic, lignoceric, undecylenic, myristoleic, palmitoleic, oleic, linoleic, eleostearic, arachidonic, ricinoleic, 9*,l0-dihydroxystearic, IO-chlorostearic, 9,10- dichlorostearic, beta-phenylpropionic, 10 phenylundecanoic, or 9,10-dibenzylstearic acid, and wherein the monoor poly-carboxylic acid component (c) is a monocarboxylic acid of from 2 to 4 carbon atoms or a polycarboxylic acid of from 4 to 6 carbon atoms; wherein component (a) is contained in an amount of from 2 to 6 grams per liter of bath, component (b) is contained in an amount of from 2 to 8 grams per liter of bath, and component (c) is contained in an amount of from 1 to 60 grams per liter of bath; and wherein the weight ratio of component (c) to components (a+b) is from about 0.1:1 to 2:1.

13. [Etching bath as claimed in claim 11 wherein the carboxylic acid of component (c) is at least one member of the group consisting of acetic acid, lactic acid, glycolic acid, oxalic acid, malonic acid, succinic acid, malic acid, maleic acid, glutaric acid, adipic acid, sebacic acid, itaconic acid and citric acid.

14. Etching bath as claimed in. claim 11 wherein the carboxylic acid of component (c) is a mono-carboxylic acid of from 2 to 4 carbon atoms.

15. Etching bath as claimed in claim 11 wherein the carboxylic acid of component (0) is a polycarboxylic acid of from 4 to 6 carbon atoms.

16. Etching bath as claimed in. claim 11 wherein the carboxylic acid of component (c) is maleic acid.

17. Etching bath as claimed in. claim 11 wherein the carboxylic acid of component (0) is citric acid.

18. Etching bath as claimed in claim 11 comprising water, nitric acid, ll-sulfo-oleic acid, at least one member of the group consisting of oleic acid, isostearic, and caprylic acid, and at least one member of the group consisting of malic acid, maleic acid, and citric acid.

19. Etching bath as claimed in claim 11 wherein one or more of components (a) to (c) is formed in situ in the bath.

20. Etching bath as claimed in claim 11 wherein from 1 1 about 30 to 100 parts by weight of nitric acid are present i FOREIGN PATENTS J i Per of [(a) 1,074,979 4/1954 France l e-14 21. Method of etching a plate of magnesium or alloys v thereof which comprises bringing the plate into etching J. H STEI NBERG, Prlmary- Examiner- C tactwith an etching bath as claimed in claim 11. 5 Us. CL

A References Cited --79-4 UNITED STATES PATENTS 1,994,500 3/1935 Boilev" 25249.4 3,234,137 2/1966 Lernaire et a1. 252-794 10 V M'rIsfi STATES PATENT 0mm CERTIFICATE OF (IQRRECTEQN Patent No. 3 725 ,159

lnventofls) Harold J. Messerschmidt et a1 natediggi l ji 1973 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1 line 23 For read

line 63 For 7 7 read Column 2 lirne 3 Column line" 3 and/or "explained" expanded Ho n II not" mOSC Fo "myristicoleic" read myristoleic FORIf FO- MSO (10-69) 'T "a, i i

UNmmras'm'ms PA'I'ICNT OFFKHL'I 4 P g T C E RT 'i. F1 (1 AT E OF 7 (1O RRE CT i G N Patent No. 3,725,159 Dam April 3, 1973 Inventor 5 Harold J."Messerschmidt et a].

It is certified that error appears in the ab0vc-idcntificd patent and that said Letters Patent are hereby corrected as shown below:

Column 7 line 54 For I e.g. U.S. Patent Nos. 3,227,166;

read i V in abbve US. Patent No;

2,669,048 elongated Signed and sealed this 13th day of November 1973.

(SEAL AtteStI EDWARD M. FLETCHER,JR. E D- TEGTMEYER Attesting Officer Acting Commissioner of Patents FORM PO-1050 0-6 USICOMM-DC 60376 r us. GOVERNMENY rnnmm: OFFICE: nu 0-4"- 

